① How long does it take to get to school?
②It takes me ten minutes.
这两个句子中it是形式主语,代替动词不定式to get to school,动词不定式作主语一般用it代替,避免主语太长,而谓语太短,出现头重脚轻的现象.
③How far is it from your home to school?
④It is 5 kilometer.
这两个句子中的it指距离,it可以指距离,时间等作主语
例如：what time is it?
what day is it today?